The turn of the twentieth century has witnessed the continued appearance of new pathogens as well as the development of antibiotic resistance and re-emergence of old pathogens. Although the war on infectious diseases was once declared over, numerous factors have conspired to make bacterial pathogens a persistent threat. Despite the enormous burden that bacterial pathogens impose on human health, there is relatively little understanding of host-pathogen interactions. In understanding the molecular details of such interactions, we will gain insight into eukaryotic cell biology. In addition, this knowledge is of vast practical importance, as it is directly relevant to disease prevention and treatment. The goal of this grant proposal is to conduct high-throughput screens using RNA interference (RNAi) to identify host factors involved in the entry and replication of the intracellular pathogen Listeria monocytogenes in Drosophila S2 cells. These screens will be complemented with compound libraries' screens to identify small molecules that affect bacteria uptake, the ability of bacteria to establish their intracellular niche, or the ability of bacteria to survive and divide. By combining the two approaches and developing high throughput assays that survey host-pathogen interactions between Listeria and Drosophila cells, we anticipate identifying genes that are important in bacterial entry, reorganization of vesicle transport, cytoskeletal rearrangements, microbial killing, bacterial nutrition, host cell death, and immune recognition. [unreadable] [unreadable] [unreadable]